The present invention relates to light emitting devices particularly those having a structure comprising a layer of organic light emitting material arranged on a substrate.
Conventional light emitting devices having a structure comprising a layer of organic light emitting material arranged on a substrate invariably comprise a substrate, a transparent electrode, a layer of organic light emitting material and a second electrode, arranged in that order. In such light emitting devices, holes are injected into the light emitting material from one electrode (usually the transparent electrode) and electrons are injected from the other electrode. Electron-hole recombination in the light emitting, or active, material generates light. The generated light is emitted from the device through the transparent electrode and substrate. These conventional devices have low efficiency, and provide a rather general spectrum output of relatively low intensity. Although not desirable, these characteristics can be tolerated in some applications but are fatal in applications such as optical communications.
It is an object of the present invention to provide a light emitting device having a structure comprising a layer of organic light emitting material arranged on a substrate, in which the above mentioned disadvantages are mitigated.
According to a first aspect of the present invention there is provided a light emitting device comprising a substrate having first and second regions, a first non-transparent electrode formed on the substrate in the first region, a layer of organic light emitting material provided over the first non-transparent electrode in the first region, a layer of organic light emitting material provided over the substrate in the second region, the light emitting materials each having at least one planar surface which is corrugated, a second non-transparent electrode formed over the light emitting material in the first region, and a mirror formed over the light emitting material in the second region.
According to a second aspect of the present invention there is provided a light emitting device comprising: a substrate having first and second regions; a first, non-transparent, electrode formed on the substrate in the first region; a first layer of organic light emitting material provided over the first electrode in the first region; a first layer of organic light emitting material provided over the substrate in the second region; the first layers of light emitting material each having at least one planar surface which is corrugated; a second electrode formed over the first layer of light emitting material in the first region; a layer of electrically insulating material formed over the second electrode in the first region; a layer of transparent material formed over the first layer of light emitting material in the second region; a third electrode formed over the electrically insulating material in the first region; a second layer of organic light emitting material provided over the third electrode in the first region; a second layer of organic light emitting material provided over the layer of transparent material in the second region; the second layers of light emitting material each having at least one planar surface which is corrugated; a fourth, non-transparent electrode formed over the second layer of light emitting material in the first region; and a mirror formed over the second layer of light emitting material in the second region.
According to a third aspect of the present invention there is provided a method of manufacturing a light emitting device comprising the steps of providing a substrate having first and second regions, providing a first non-transparent electrode on the substrate in the first region, providing a layer of organic light emitting material over the first non-transparent electrode in the first region, providing a layer of organic light emitting material over the substrate in the second region, providing each of the light emitting materials with at least one planar surface which is corrugated, providing a second non-transparent electrode over the light emitting material in the first region, and providing a mirror over the light emitting material in the second region.
According to a fourth aspect of the present invention there is provided a method of manufacturing a light emitting device comprising the steps of: providing a substrate having first and second regions; providing a first, non-transparent, electrode on the substrate in the first region; providing a first layer of organic light emitting material over the first electrode in the first region; providing a first layer of organic light emitting material over the substrate in the second region; providing each of the first layers of light emitting material with at least one planar surface which is corrugated; providing a second electrode over the first layer of light emitting material in the first region; providing a layer of electrically insulating material over the second electrode in the first region; providing a layer of transparent material over the first layer of light emitting material in the second region; providing a third electrode over the electrically insulating material in the first region; providing a second layer of organic light emitting material over the third electrode in the first region; providing a second layer of organic light emitting material over the layer of transparent material in the second region; providing each of the second layers of light emitting material with at least one planar surface which is corrugated; providing a fourth, non-transparent, electrode over the second layer of light emitting material in the first region; and providing a mirror over the second layer of light emitting material in the second region.
In stark contrast to the conventional arrangements the present invention provides a light emitting device in which an active layer provided on a substrate is sandwiched between two non-transparent electrodes.
It is understood that proposals have been made for the use of corrugated surfaces within certain electronically pumped laser devices. However, such devices have a fundamentally different structure and mode of operation compared with the light emitting devices to which the present invention applies. Moreover, the previous proposals have been of a mainly theoretical nature and have postulated devices which would be extremely difficult, if not impossible, to fabricate in practice.